page_title: Pinacosaurus
section_title: Skeleton
hierarchical_section_title: Pinacosaurus / Description / Skeleton
caption_attribution_description: English: Mounted skeleton of Pinacosaurus specimen MPC 100/1305 with skull cast of Saichania. Central Museum of Mongolian Dinosaurs.
context_page_description: Pinacosaurus is a genus of ankylosaurid thyreophoran dinosaur that lived in Asia during the Late Cretaceous, mainly in Mongolia and China.
  The first remains of the genus were found in 1923, and the type species Pinacosaurus grangeri was named in 1933. Pinacosaurus mephistocephalus named in 1999, is a second possibly valid species differing from the type species in details of the skull armour. Of Pinacosaurus grangeri many skeletons have been found, more than of any other ankylosaur. These predominantly consist of juveniles that perhaps lived in herds roaming the desert landscape of their habitat.
  Pinacosaurus was a medium-sized ankylosaurine, about five metres long and weighed up to two tonnes. Its body was flat and low-slung but not as heavily built as in some other members of the Ankylosaurinae. The head was protected by bone tiles, hence its name. Each nostril was formed as a large depression pierced by between three and five smaller holes, the purpose of which is uncertain. A smooth beak bit off low-growing plants that were sliced by rows of small teeth and then swallowed to be processed by the enormous hind gut.
context_section_description: The adult skulls known have a length of about thirty centimetres. Pinacosaurus has exceptionally smooth praemaxillae, front snout bones, forming the bone core of the upper beak, that was in life covered with a horn sheet. The maxilla bears about fourteen teeth. A typical and remarkable element of ankylosaurine skulls is that the nostril is in the shape of a large "narial vestibule" in which several smaller oval holes are present. With Pinacosaurus there are at least three per side. Gilmore already noticed this configuration in the original specimen. To allow a comparison between the holes of the several ankylosaurine species, they have been dubbed "A", "B" and "C". The top hole A seems to access the main air-passage of the nasal cavity. In P. grangeri this hole is visible in top view through a notch in the snout armour, whereas in P. mephistocephalus the armour overhangs the hole. The opening pattern is characteristic of the genus: in Pinacosaurus the C hole is below the A hole and the B opening is on the lower outer side of the vestibule. In Pinacosaurus juveniles the C hole seems to consist of secondary smaller openings of varying number: Godefroit et al. described four pairs of openings in total in 1999, and in 2003 a juvenile specimen with five pairs of openings was described. The extra C openings have been named C2 and C3. The precise function of this arrangement is unclear. There are several chambers in the praemaxilla and maxilla to which these holes are connected but it has also been suggested that some extra holes are the result of damage. The larger number with juveniles could be explained by cartilage sheets not having been ossified yet.
  The visible sutures of the skull elements in juvenile specimens allowed for the first time to determine their precise arrangement. They generally consisted of indistinctly formed simple shapes. Several skull openings like the antorbital fenestra and the temporal fenestrae apparently closed at a very young age for they are no longer visible even in the juveniles found. The squamosal horn does not cover the entire squamosal, creating the illusion that an additional skull bone is present in front of the horn. Maryańska in 1977 thought that this was a tabular bone, otherwise unknown in dinosaurs, proving that the Ankylosauria had independently evolved from the Aetosauria, a hypothesis today entirely discarded. Godefroit in 1999 called it a "secondary dermal squamosal". A real distinctive trait is that the quadratojugal touches the postorbital, whereas in other Thyreophora for which the condition is known, these bones are separated by the jugal. Usually it is assumed that this configuration is not unique for Pinacosaurus but a synapomorphy of the Ankylosauridae as a whole.
  In 2015, a juvenile specimen was described showing a complex hyoid bone or tongue bone apparatus. It included paraglossalia at the sides, paired first and second ceratobranchials and higher epibranchials. Also the bone structure suggested that in the middle a cartilaginous basihyal was present. The strong development of the hyoid would indicate that a powerful tongue compensated for the weakly developed dentition. It was inferred that all dinosaurs had such complex tongue bones but that these were generally lost during fossilisation.
   
  The postcranial skeleton of the known fossils is rather lightly built. Most of these represent juveniles, however: even specimen IMM 96BM3/1, the P. mephistocephalus holotype, is no longer than about 3 m (9.8 ft). Juveniles had four rear back vertebrae fused into a "sacral rod", three true sacrals, and a tail base of seven vertebrae possessing transverse processes. Behind these about eight "free" vertebrae are present, followed by about twenty vertebrae stiffened by projections and forming the "handle" of the tail club. Like all ankylosaurids, Pinacosaurus had a bony club at the end of its tail which it likely used as a defensive weapon against predators. This club was relatively small.
  The torso is very flat. The forelimbs are moderately robust; the P. mephistocephalus holotype ha
caption: MPC 100/1305 with Saichania skull cast, showing armour on back and limbs
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